In recent years, attention has been focused on a technique using so-called terahertz-waves. Spectral analysis using terahertz-waves, imaging using terahertz-waves, and the like have been expected for industrial applications.
For example, techniques now under development in application fields of terahertz-waves include an imaging technique using a safe fluoroscopic apparatus as an alternative to an X-ray apparatus, a spectral technique for obtaining an absorption spectrum or complex dielectric constant of a substance to examine a bonding state therein, a technique for analyzing biomolecules, and a technique for estimating a carrier concentration or mobility.
Of the techniques, as a method of spectroscopically analyzing a substance using terahertz-waves, there has been known a method of irradiating a substance to be analyzed with terahertz-waves to obtain a spectrum of transmitted or reflected terahertz-waves.
Meanwhile, water has regions of very strong absorption in the frequency range of 30 GHz to 30 THz. Therefore, terahertz-waves are almost blocked out by, for example, a container with a thickness of 1 mm containing liquid water. Thus, it is relatively difficult to obtain information about a substance contained in water by means of terahertz-waves that have passed through the water.
Therefore, as a method of determining an absorption spectrum or complex dielectric constant of a substance such as water having a strong absorption spectrum band within the terahertz range or molecules contained in such a substance, there has been known a method using an evanescent terahertz-wave which is generated in total reflection in a prism, as disclosed in “Extended Abstracts, The 51st Spring Meeting, 2004, The Japan Society of Applied Physics and Related Societies, 28p-YF-7”. In this method, terahertz-waves emitted from a terahertz-wave generator are made incident on a first surface of a prism and totally reflected by a second surface of the prism. Then, terahertz-waves that have exited from a third surface of the prism are detected by a detector, and a sample is disposed on the second surface so as to interact with an evanescent terahertz-wave which is generated upon the total reflection of the terahertz-waves by the second surface, thereby spectroscopically analyzing the sample. According to this method, it is possible to analyze a sample in a form of solid, powder, liquid, or the like. However, because the method disclosed in “Extended Abstracts, The 51st Spring Meeting, 2004, The Japan Society of Applied Physics and Related Societies, 28p-YF-7” uses a spatial optical system, system size reduction as well as optical adjustment is difficult.